Tidal Hypothesis of James Jeans | Tides| Geography

Sir James Jeans, a British scientist, propounded his ‘tidal hypothesis’ to explain the origin of the earth in the year 1919 while another British scientist, Harold Jeffreys, suggested modifications in the ‘tidal hypoth­esis’ in 1929 and thus made it more relevant and significant in the context of increasing knowledge of the cosmogonic ideas of the 1st quarter of the 20th century. Tidal hypothesis is one of the modern hypotheses of the origin of the earth and the solar system.

Jeans postulated his hypothesis on the basis of certain axioms (self-proved facts) as given below:

(1) The solar system was formed from the sun and another intruding star.

(2) In the beginning the sun was a big incandes­cent gaseous mass of matter.

(3) Besides the sun, there was another star termed as ‘intruding star’ in the universe. This intrud­ing star was much bigger in size than the primitive sun.

(4) The primitive sun was stationary and was rotating on its axis.

(5) The ‘intruding star’ was moving along such a path in such a way that it was destined to come nearer to the primitive sun.

(6) There was a great impact of the tidal force of the intruding star on the surface of the primitive sun.

James Jeans postulated that due to massive gravitational force of the ‘intruding star’, huge amount of matter was ejected from the primitive sun, which later on became the building material of future planets. According to the Newton’s law of universal gravita­tion (1687) everybody in the universe attracts every other body with a force which is directly proportional to the product of the masses of the two bodies and inversely proportional to the square of the distance between them.

It means that the intensity of the gravi­tational force of the ‘intruding star’ and the ‘primitive sun’ would depend upon two factors e.g.:

(i) Product of the masses of the intruding star and the primitive sun, and

(ii) The distance between the two stars.

There is direct relation between the product of the masses of the ‘intruding star’ and the primitive sun (equation 3). Gravitation a Product of the Force mass of the two stars………….. (3)

It means that if the product of the masses of the ‘intruding star’ and the ‘primitive sun’ is high, the amount of gravitational force between them will also be high and if the product of masses of the two stars is low the amount of gravitational force will also be low. In simple words, it also means that if the mass of the ‘introding star’ is high, the gravitational force exerted by it will also be high.

Since James Jeans assumed the ‘intruding star’ to be much bigger than the ‘primitive sun’, the former exerted larger amount of gravitational pull on the surface of the ‘primitive sun’ than the gravitational pull of the ‘primitive sun’ which caused ejection Of matter from the ‘primitive sun’.

Secondly, there is an inverse relation between the gravitational force of two stars and the distance between them (equation 4).

It means that as the distance between two stars decreases, the amount of gravitational force between them increases and as the distance between two stars increases, the gravitational force between them de­creases. Since the ‘intruding star’ was coming closer to the ‘primitive sun’ and hence the amount of gravita­tional force between them was also increasing.

Evolution of filament:

According to James Jeans the ‘intruding star’ was continuously moving along such a path that it was coming nearer to the primitive sun and thus exerted gaseous tidal force (gravitational pull) on the surface of the ‘primitive sun’. As the ‘intruding star’ came nearer and nearer to the ‘primi­tive sun’, its gravitational force went on increasing with the result tidal force also increased.

When the ‘intruding star’ came nearest to the ‘primitive sun’ its gravitational force became maximum, with the result a giant cigar-shaped tide, thousands of kilometres in length, was created on the outer surface of the ‘primi­tive sun’ and ultimately huge mass of matter, in the shape of a cigar, was ejected from the ‘primitive sun’. James Jeans called this cigar-shaped matter as filament which was much thicker in the centre and thinner and sharper at the ends (tapering ends) (see fig. 2.1).

The shape of the ejected filament with thick middle portion and tapering ends may be explained in the following manner:

(i) When the ‘intruding star’ was at distant place from the ‘primitive sun’ (but not so distant that it could not exert attractional pull on the surface of the ‘primi­tive sun’) the gravitational attraction exerted by it on the surface of the primitive sun was also low due to greater distance between them. Therefore small quan­tity of the First part of the incandescent matter came out from the surface of the primitive sun.

(2) When the intruding star came nearest to the primitive sun, maxi­mum amount of gravitational attraction was exerted by it on the surface of the primitive sun due to minimum distance between them. This attractional and tidal force resulted into the ejection of maximum amount of the incandescent matter (which represented the middle portion of the filament).

(3) When the ‘intruding star’ moved away from the primitive sun (but not so away that it could not exert attractional pull on the primitive sun), the gravitational attraction exerted by it on the primitive sun became low due to greater distance between them.

Thus, again small quantity of incandes­cent matter came out from the surface of the primitive sun. Thus, the shape of matter ejected from the primi­tive sun became like a cigar which was called by James Jeans as ‘filament.’

(4) Gradually and gradually the intruding star moved far away from the primitive sun and thus went out of the domain of the gravitational field of our primitive sun. In the beginning, when the filament was detached from the primitive sun it fol­lowed the intruding star as it was pulled by the intrud­ing star.

The filament tried to keep pace with the intruding star for some time but could not succeed and ultimately it (filament) started revolving around the primitive sun.

Formation of planets from the filament:

Accord­ing to James Jeans nine planets of our solar system were formed due to cooling and condensation of the incandescent mass of gaseous matter of the filament. The filament, after being detached from the sun, began to cool down. Thus, the filament started contracting in size on cooling. The contraction of the filament led to its breaking in several pieces and each piece was condensed to form one separate planet. This process led to the formation of nine planets.

The filament of incandescent gaseous matter allowed bigger planets to form in its middle portion (like Jupiter and Saturn) and smaller ones towards its tapering ends. The remaining part of the primitive sun became our sun. The satellites of the planets were formed due to gravitational pull and tidal effect exerted by the sun on the outer surfaces of the newly formed planets.

The processes of the formation of satellites cased when the amount of matter ejected from the planets for the formation of new satellites became so low that it was not able to hold together its matter by its central gravitational force/attraction.

The rate of cool­ing of the primitive incandescent gaseous planets was dependent upon the size of the planet. The planets of greater mass cooled very slowly while the smaller planets and satellites condensed to liquid and then to solid forms within very short period. This may be the possible reason for larger number of satellites of bigger planets and fewer number of satellites of smaller plan­ets.

Very small planets were cooled and condensed soon, so no matter could be ejected from their surface due to tidal effect and thus no satellite could be formed. This is why Mercury, Venus and Pluto do not have any satellite.

Evidence in Favour of the Hypothesis:

The ‘tidal hypothesis’ of James Jeans has not only explained the origin of the solar system and the earth but has also attempted successfully to some extent, to solve various problems of the solar system related to its shape, size, structure and peculiar motion.

The following characteristics of the solar system are more or less explained on the basis of this hypothesis:

(1) Shape and Ordering of Planets:

The filament ejected from the primitive sun was cigar-shaped. It was thick in the middle portion and thin at the ends. The planets formed from the condensation of the incandescent gaseous matter of the middle portion of the filament were bigger in size than the planets formed from the condensation of matter at the tapering ends of the filament (fig. 2.2).

This arrangement of the planets formed of the filament clearly matches with the present planetary arrangement of our solar system. If we start from the sun, the size of the planets (Mercury, Venus, Earth, Mars-which is an exception) increases upto Jupi­ter which is the biggest planet and occupies almost the central position in the solar system.

The size of the planets after Jupiter (Saturn, Uranus, and Naptune) again decreases till the location of the smallest planet- Pluto at the extreme end. It may be pointed out that James Jeans propounded his hypothesis before the discovery of Pluto. Thus, the discovery of planet Pluto having smallest size and its location at the extreme end further enhanced the significance of tidal hypothesis.

(2) Ordering and Arrangement of Satellites:

Ac­cording to this hypothesis the satellites of the planets were formed through the condensation of incandescent gaseous matter ejected from the planets in the same manner as the planets were formed through the condensation of incandescent gaseous matter ejected from the sun. Thus, there is almost the same type of arrange­ment of satellites around the planets as is the arrange­ment of planets around the sun in our solar system i.e. smaller ones at the end and bigger ones in the middle.

For example, if a planet has several satellites, the biggest satellite is placed in the middle and smaller ones arc placed at the end. The arrangement of satel­lites of Jupiter and Saturn confirms the above fact.

(3) Number and Size of Satellites:

According to tidal hypothesis bigger planets remained in gaseous form for longer time in the space because their cooling took longer time due to their large size. On the other hand, smaller planets were cooled and condensed within very short period of time because of their small size.

Thus, larger number of satellites were formed from bigger planets but the size of such satellites was relatively small whereas fewer number of satellites were formed from medium-sized planets but the size of such satellites was relatively larger. Very small planets occupying the end location of planetary system were cooled and condensed within very short period of time and hence no satellites could be formed from them. The existing planetary arrangement of the solar system confirms the above fact.

For example, Jupiter and Saturn (biggest planets) have 14 and 15 satellites respectively while Mercury, Venus and Pluto, which are smallest planets of our solar system do not have any satellite (table 2.1).

(4) Rotation, revolution and inclination of the planets’ axis:

According to James Jeans the planets were formed from the filament which was revolving around the sun. Thus, the planets of our solar system should also revolve around the sun. In our present day solar system all the planets are revolving around the sun in the same direction and also in the same orbital plane (the orbital plane of Pluto is however slightly inclined).

Similarly, almost all their satellites of the planets are also revolving around their respective plan­ets in the same direction as their father planets are revolving around the sun. James Jeans also proposed that the rotational motion of the planets should also be in the same direction. Except Venus and Uranus all the planets of the present solar system rotate on their axis in the same direction as their revolution around the sun.

As per tidal hypothesis the encounter of the primitive sun and the intruding star was not in the same planes of their rotation. The filament, which was ejected from the primitive sun by the gravitational attraction of the intruding star, was slightly inclined. Thus the axis of rotation of the planets, which were formed from the inclined filament (inclined from the plane of the rota­tion of our sun), should also be inclined. It is apparent from table 2.1 that all the axes of the planets of the present solar system are inclined. However, the planes of the orbital paths of various planets are also not matching with the plane of rotation of our sun.

Modification by Jeffreys:

Harold Jeffreys, a British scientist, modified the original tidal hypothesis of James Jeans in 1929 and presented his concept as ‘collision hypothesis’. Accord­ing to Jeffreys there were three stars in the universe before the origin of our solar system. One was our primitive sun, the second one was its ‘companion star’ and the third one was ‘intruding star’ which was moving towards ‘companion star’.

Thus, the intruding star collided against the ‘companion star’. Due to head-on collision the companion star was completely smashed and shattered, some shattered portions were scattered in the sky while remaining debris started revolving around the primitive sun. However, the impact of collision and explosion enabled the intruding star to clear itself off from the gravitational attraction of the primitive sun and gradually vanished in the universe.

The planets of our solar system were formed from the remaining debris of the companion star. It may be pointed out that Jeffreys suggested modifications in the tidal hypothesis of James Jeans with the intention to remove major inherent weak points of the tidal hypothesis so that it can withstand the criticisms of the modern scientific world.

Evaluation:

The tidal hypothesis as propounded by James Jeans and modified by Harold Jeffreys enjoyed a long lease of popularity and wide appreciation till the end of the 1st half of the 20th century because of its simplic­ity, inherent logic and scientific appeal but the hypoth­esis was severely criticised on various grounds. Even Jeffreys accepted in Guttenberg (1951) that his modi­fied version of tidal hypothesis needed substantial modifications and in some places was completely wrong.

The following criticisms have been labelled against this hypothesis:

(1) According to B. Levin the universe is infi­nite in space and time and the stars are so distant from each other that such a close encounter between them is a remote possibility.

(2) James Jeans did not explain the where about and destiny of the intruding star/which caused tidal, eruption on the surface of the primitive sun in the form of filament.

(3) N.N. Parisky has proved on the basis of mathematical calculation that tidal hypothesis fails to explain the real distances between the sun and the planets in our present solar system. Hoyle has main­tained that if ‘we reduce the solar system to scale, representing the sun by a ball of the size of a large grape fruit, the bulk of the planetary material lies at a distance of some 100 yards from it.’

That is why American astronomer Russell expressed serious doubts about the fact that such a huge amount of material of the filament would have come out from the primitive sun to form planets at much greater distances from the sun, some times more than 500 to 3000 times the diameter of the sun (the distances of Jupiter and Naptune from the sun respectively). In fact, according to this hypothesis the planets should have been very close to the sun but in reality they are far away from the sun.

(4) According to Wooldrige and Morgan ‘the fundamental difficulty is that the planets comprising but a small fraction of the total mass of the system, yet at great distances from the sun, carry most of the angular momentum of the system’. Many modern astrophysicists are of the opinion that the angular momentum imparted by the intruding star to the plan­ets was not high enough to match the existing angular momentum of the planets of our present solar system.

(5) The planets of our solar system are largely formed of the elements having high atomic weight but the constituent elements of the sun (from which the planets are supposed to have been formed) are of lighter atomic weight e.g. hydrogen and helium. The tidal hypothesis fails to offer convincing explanation for such anomalous situation,

(6) Another problem is that of the formation of satellites from the planets. If for the time being we accept the view that satellites were formed from the tidal effect exerted by the primitive sun on the newly born planets, then question arises, why no satellite was formed from Mercury and Venus though these planets were nearest to the sun.

In the circumstances the sun should have exerted maximum gravitational force on the outer surfaces of Mercury and Venus. The argu­ment that small planets were condensed to solid form within very short period of time and hence there was no time for the ejection of matter from these planets does not appear sound.

(7) James Jeans could not elaborate the process and mechanism of the condensation of matter ejected from the primitive sun.